This invention relates to a bone graft, to a method of making the bone graft and to a guided bone regeneration (GBR) method employing the bone graft. More particularly, this invention relates to an implantable, biocompatible osteogenic bone graft possessing at least one zone of impermeability to soft tissue ingrowth, to a method of making such bone graft and to a guided bone regeneration method that promotes bone cell ingrowth preferentially over soft tissue ingrowth.
Conventionally, bone tissue regeneration is achieved by filling a bone repair site with a bone graft. Over time, the bone graft is incorporated by the host and new bone remodels the bone graft. The bone grafts currently in use, however, do not always provide reliable bone tissue regeneration because they are not capable of inducing sufficient bone growth before competitive, faster-growing soft tissue and epithelial cells fill the bone repair site. To overcome this problem, current standard procedures employ a barrier material which is applied over the bone graft to exclude competitive cells. This procedure is known as guided bone regeneration (GBR) or guided tissue regeneration (GTR) and is documented to be useful as an adjunct to the bone graft procedure.
By way of example, a common problem in periodontal surgery is maintenance of bone tissue around teeth or in those areas where teeth have been removed and dental implants will subsequently be placed. Demineralized bone matrix (DBM) is a common material used to promote bone formation in these areas. DBM works well due to its osteoinductive and osteoconductive healing properties. A common practice is to extract a tooth and then place DBM back into the socket such that new bone will then grow into the socket allowing a solid foundation for subsequent metallic implant placement. A common adjunct to this procedure is the placement of a barrier membrane over the surface of the bone graft such that ingrowth of soft tissue from the gingiva and other surrounding areas can be prevented.
Several problems are associated with barrier membranes. Their surgical placement is tedious, they have a tendency to become infected and they are relatively costly. After the initial surgical procedure, removal of the membrane to prevent effects such as inflammation and infection is required. A well known commercially available membrane is made of expanded polytetrafluoroethylene (e-PTFE) film by WL Gore, Inc. Recently, bioabsorbable membranes fabricated from collagen or other polymers such as polyglycolates have become available. While these membranes obviate the need for a subsequent removal operation, they are difficult to handle and implant and do not always remain intact long enough to initiate sufficient bone growth.
It is an object of the present invention to provide a bone graft which promotes bone cell ingrowth preferentially over soft tissue ingrowth in a bone repair procedure.
It is a further object of the present invention to provide a bone graft which promotes bone cell ingrowth below the bone line and prevents soft tissue ingrowth above the bone line in a bone repair procedure.
It is yet a further object of the present invention to provide a GBR method which obviates the need for a barrier membrane in a bone repair procedure.
It is yet an even further object of the present invention to provide a bone graft which occludes soft tissue ingrowth while promoting bone formation within the bone repair site.
It is still a further object of the present invention to provide a bone graft possessing rigidity in order to maintain space for the bone formation zone. Rigidity prevents displacement due to loads placed on the bone repair site.
In keeping with these and related objects of this invention, an implantable, biocompatible osteogenic bone graft is provided which comprises at least one zone of impermeability to soft tissue ingrowth wherein said zone is integral with the bone graft. The bone graft of this invention can be formed by providing a coherent mass of bone particles and occluding a portion of a surface of the coherent mass of bone particles to provide a zone of impermeability to soft tissue ingrowth on such surface.
Application of the foregoing bone graft to a bone repair site leads to selective rapid new bone ingrowth and inhibits or prevents soft tissue, e.g., gingival, epithelial, connective and/or muscle tissue, ingrowth in those areas adjacent to the zone(s) of impermeability to soft tissue ingrowth.
The term xe2x80x9ccoherentxe2x80x9d as applied to the mass of bone particles refers to the ability of the bone particles to adhere to each other either mechanically, e.g., by entanglement, or by use of a biocompatible matrix whether the mass of bone particles is in the dry or wetted, e.g., hydrated, state.
The term xe2x80x9costeogenicxe2x80x9d as applied to the bone graft of this invention shall be understood as referring to the ability of the bone graft to enhance or accelerate the ingrowth of new bone tissue by one or more mechanisms such as osteogenesis, osteoconduction and/or osteoinduction.
The term xe2x80x9coccludingxe2x80x9d as utilized herein shall be understood to refer to any operation or process which reduces the porosity of a surface area of the bone graft to render such surface area substantially impermeable to the ingrowth of soft tissue.
The terms xe2x80x9cimpermeablexe2x80x9d and xe2x80x9cocclusivexe2x80x9d are utilized herein interchangeably and shall be understood as referring to any zone, i.e., surface region, of the bone graft of this invention which possesses an average pore size which substantially prevents the ingrowth of soft tissue. Average pore sizes of from about 3 microns or less are known to prevent ingrowth of soft tissue. The zone of impermeability can include pores larger than 3 microns as long as the presence of such pores does not permit soft tissue ingrowth. Generally, average pore sizes above 30 microns are believed to permit soft tissue ingrowth.
The term xe2x80x9cintegralxe2x80x9d as utilized herein is intended to differentiate the bone graft of this invention from bone grafts which are combined with a separate barrier membrane material. In the instant invention, the bone graft and the zone of impermeability are integral with one another, i.e., they are formed from the same material and are indivisibly interconnected so as to form a single, unified whole.
The term xe2x80x9crigidityxe2x80x9d as utilized herein refers to the property of the bone graft of resisting displacement or deformation when load is applied thereto. This ability to hold the appropriate space is important to preserve adequate bone volume after healing occurs.